CRG20

MEMS-Gyroskope

CRG20

A low-cost miniature gyro, optimised for medium volume production programmes where high stability, performance and cost are key drivers. Available in a variety of rate ranges - +/-75°/s and +/-300°/s, plus a new high rate range (800°/s) variant. Digital (SPI®) and analogue outputs. Low drift and excellent performance over temperature

In addition to a commanded self test feature, CRG20 incorporates continuous self-testing of the complete operation of the sensor and the signal conditioning circuits. CRG20 has been designed to provide unparalleled sensor integrity, through the mitigation of potential error sources and false-plausible failure modes. System designers have the opportunity with CRG20 to eliminate the requirement for redundant sensors in high integrity applications.

The sensor provides a digital interface in the form of a SPI® port together with analogue output pins for customers who need to operate in the analogue domain. In addition, two auxiliary analogue input pins are available to digitise other sensors such as accelerometers or additional gyros; this enables multi-axis sensor clusters to be easily produced.

Product Lifecycle Status

Production Status: Limited Production
Temporary shortage: Call us to discuss CRM100-based alternatives.
Availability: Not available
Customer Applications: Existing applications only

Produktbeschreibung

A low-cost miniature gyro, optimised for medium volume production programmes where high stability, performance and cost are key drivers. Available in a variety of rate ranges - +/-75°/s and +/-300°/s, plus a new high rate range (800°/s) variant. Digital (SPI®) and analogue outputs. Low drift and excellent performance over temperature

In addition to a commanded self test feature, CRG20 incorporates continuous self-testing of the complete operation of the sensor and the signal conditioning circuits. CRG20 has been designed to provide unparalleled sensor integrity, through the mitigation of potential error sources and false-plausible failure modes. System designers have the opportunity with CRG20 to eliminate the requirement for redundant sensors in high integrity applications.

The sensor provides a digital interface in the form of a SPI® port together with analogue output pins for customers who need to operate in the analogue domain. In addition, two auxiliary analogue input pins are available to digitise other sensors such as accelerometers or additional gyros; this enables multi-axis sensor clusters to be easily produced.

The CRM100 gyro can provide a very similar performance to the CRG20 when it is being used in an analogue configuration. There have been improvements made since the parts were first released and while the data sheet figures have remained the same the typical performance has improved (8⁰/hr bias instability). By using two CRM100 and summing the output with a gain of 0.5 then the errors are generally reduced by a factor of √2 (ie 8/√2 = 5.7⁰/hr – very close to the performance of the CRG20) . These error can be reduced further by mounting one CRM100 ‘upside down’ (on the reverse of the pcb) and summing the difference of the outputs, reducing common mode errors.

Alternatively, the CRS43 (which uses the CRM100 internally) has a 5V input – the same as the CRG20.

{
/* Get a byte from the buffer and place it in SPI output register */
SPDR = Latest_Tx_SPI_Message[i];

/* Wait for the data to be sent */
while( (SPSR & (1<<SPIF)) != (1<<SPIF) );

/* Copy the received byte into the buffer */
Latest_Rx_SPI_Message[i] = SPDR;

/* N.B. For faster CPU’s place a delay in here */

}
/* Set SS line high */
PORTD = PORTD | (1<<PD2);

}

Please note that this controller is working at 3.69MHz (considerably slower than the CRG20processor) so the time it takes to check the data has been sent and copy in the received byte is equivalent to the delay needed between bytes. If a faster processor was used we would have to add a delay

It is possible that this is the result of an unintentional activation of Commanded BIT. Triggering CBITA results in a rate offset of around 10-13 deg/s being applied to the sensor output (either from the SPI digital interface or either of the analogue outputs). For this reason it is recommended that the CBITA line is pulled low if is not being used (see note 3 in CRG20-00-0100-0110 rev 9 specification).

Our devices are inherently insensitive to linear acceleration or g. The vibrating structure is a ring and is made to resonate at about 14 KHz. If the ring moves under acceleration load, the modulation and de-modulation signals and the amplitudes are not affected. Therefore we expect very little g sensitivity. When the design requirements were formulated for CRG20, the design requirement was set at 0.1 deg/s/g. Our design verification tests have confirmed very little g sensitivity at all accelerations above 4g (typically <0.0001 deg/s/g). Measurements below 4g are dominated by other error sources such as bias instability and bias and SF changes with temperature and therefore it is difficult to attribute which errors are due to g sensitivity. So when we do a g sensitivity test, we assume that all measurement errors are due to g sensitivity and this results in a very pessimistic number. Our experience is therefore that it is not necessary to compensate for g sensitivity. If you wish to confirm this for yourselves, you could try a simple +/- 1g tumble test, and average the data for about 30 seconds, to see if there are any measurable changes when the g changes from +1g to -1g. Earth rate may need to be allowed for too.

The CRG20 needs to be powered from a 5V supply. To interface it to a 3.3V system will require a special attention to the logic thresholds of both inputs and outputs from the CRG20. The logic thresholds are shown below. For inputs to the CRG20, the threshold is 0.6*5.0 or 3V. Therefore a 3.3V system shouldn’t need any level shifting if the Logic High can be guaranteed to be above 3V. Logic Low will be correctly detected. For outputs from the CRG20, the levels will have to be reduced unless the 3.3V system has “5V Tolerant” inputs. A resistor is normally all that is required to achieve this, the value of which depends on the input resistance of the 3.3V system.

We are often asked about MSL in relation to CRG20. MSL specifications are usually quoted for plastic-encapsulated components. This is because they absorb moisture which causes problems when they are subjected to soldering. In contrast, our CRG20 gyro is a ceramic, hermetically sealed package. An MSL specification is not normally quoted for such a package as it is not relevant - it does not absorb moisture.

The specification gives the temperature limits for storage and provided that this is adhered to here are no particular risks associated with the long term storage of CRG20. From the perspective of solderability, it is important to store the CRG20 in an environment that is dry, and low in sulphur, chlorine and hydrocarbons. It is accepted practice within the industry to achieve this by vacuum packing the parts in an ESD safe moisture barrier bag.